Overall, banks' clean energy investments went up 5 percent to $260 billion in 2011, but some doubt that the investment will remain as high in the future, as a U.S. Treasury funding program that provides grants for up to 30 percent of renewable energy projects comes to an end, according to Bloomberg Markets.

But the green banks rankings may also be bad news for another oft-derided financial institution: Goldman Sachs. The investment bank dropped 16 spots, falling from second to eighteenth in the green bank rankings.